Conventionally, as in Patent Document 1: Japanese Unexamined Laid-open Patent Application Publication No. 2006-191782 which is hereinafter incorporated into the conventional art, as an electric motor used as a driving force for, e.g., various electric vehicles including electric motorcycles and various electric products, a radial gap type electric rotating machine and an axial gap type electric rotating machine are widely known. The radial gap type electrical rotating machine includes a rotor having permanent magnets and configured to rotate about a rotation axis and a cylindrical stator having stator windings and arranged in a radial direction of the rotor via a gap. On the other hand, the axial gap type electrical rotating machine includes a stator having stator windings and a circular disc shaped rotor having permanent magnets and arranged on one end side of the stator in the axial direction of the stator via a gap.
In recent years, a small and high-performance electric motor as a driving force for various electric vehicles including electric motorcycles has been desired. In this type of the electric motor, if the operational range from a high torque low revolution speed range to a low torque high revolution speed range is wide, a driving force required for a vehicle operation can be obtained without using a transmission normally required for a vehicle with an internal combustion engine. When considering mounting such a motor on a vehicle, it is preferable that the size of the electric motor is as small as possible. Therefore, in order to attain a small and high-performance electric motor, it is preferable to arrange as many windings as possible in the limited winding arrangeable region of the stator, and various proposals have been made. According to some proposals, it is said that the space factor of the winding has been improved and therefore a compact electric motor capable of generating a high torque can be provided.
Due to characteristics of an electric motor, however, an electric motor has a problem that although a high torque can be generated in a low revolution speed range, the upper limit of the revolution speed will be limited in a high revolution speed range. That is, in an electric motor, although a high torque can be generated in a low revolution speed range, as the number of revolutions increases, the induced voltage (i.e., back electromotive force), which is to be generated at the stator winding arranged on the stator by a magnetic flux of the permanent magnet provided at the rotor, increases. When the revolution speed increases and reaches a certain speed, the induced voltage induced at the stator winding becomes equal to the applied voltage of the electric motor, preventing the electric current flow in the stator winding. This in turn prevents a further increase of the revolution speed. To solve this problem, it is performed, for example, to decrease the induced voltage (i.e., back electromotive force) by performing a field weakening control.
The field weakening control, however, requires an additional electrical power to negate the induced voltage. Therefore, in the case of a product having an electric motor used in a state in which an electric power is supplied from the outside, the increased power consumption does not result in a shortened drivable time. However, in the case of a product, such as, an electric motorcycle driven by a battery mounted thereon, since the battery capacity is limited, the electric current supplied to negate the induced voltage induced to the stator winding causes increased electric power consumption, resulting in a shortened drivable time. For this reason, it is requested to decrease the power consumption as much as possible.
The inventors proposed a new structure of a stator capable of eliminating the need for a field weakening control which induces additional power consumption. In this proposal, a tooth portion of a stator on which a winding is arranged is divided into at least two divided tooth portions in a relatively movable manner so that the relative movement thereof changes the flow of magnetic flux to decrease the flux linkage of the stator winding at the time of a high revolution speed. According to this proposal, since the flux linkage of the stator winding at the time of a high revolution speed can be adjusted by a physical means, the electrical power conventionally required for the field weakening control can be decreased or eliminated, which enabled to provide an electrical rotating machine capable of decreasing power consumption.
In such an electrical rotating machine having the aforementioned structure, it is desired to further enlarge the operational range from a high torque low revolution speed range to a low torque high revolution speed range.